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Introduction à l’épidémiologie

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1 Introduction à l’épidémiologie
IFSI UE1.2-S2 Introduction à l’épidémiologie Maxime Desmarets Interne Santé Publique et Médecine Sociale, UFR SMP, Besançon Cours enregistré en janvier 2013 UE 1.2.S2 - Épidémiologie

2 Sommaire Définition Historique Utilisation de l’épidémiologie
Branches de l’épidémiologie Considérations éthiques Epidémiologie et pratique des soins infirmiers UE 1.2.S2 - Épidémiologie

3 Introduction à l’épidémiologie
1. Définition

4 Epi – demos – logos Sur – le peuple – l’étude de
L’épiémiologie. Qu’est ce que c’est? Que’est ce que ca veux dire ? D’abord ca vient du grec , le mot peut se décmposer en épi-démos-logos. Epi ca veut dire sur, au dessus. Démos, ca veut dire le peuple, mais aussi le pays, et logos comme dans tous les mots en ‘logues’ comme psychologue, ca veux dire l’étude de. Donc si on résume épidémiologie c’est l’étude des évènements qui se produisent sur le peuple ou sur le pays. UE 1.2.S2 - Épidémiologie

5 “L’épidémiologie est l’étude de la distribution et des déterminants des états ou des événements liés à la santé dans des populations spécifiques, et l’application de cette connaissance pour le contrôle des problèmes de santé.” Last JM, editor. Dictionary of epidemiology. 4th ed. New York: Oxford University Press; p. 61. UE 1.2.S2 - Épidémiologie

6 « Etude » discipline scientifique
“la science de base de la santé publique” Surveillance, observation, tester des hypothèses, recherche analytique, expérimentation Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation. Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. Basic epidemiologic methods tend to rely on careful observation and use of valid comparison groups to assess whether what was observed, such as the number of cases of disease in a particular area during a particular time period or the frequency of an exposure among persons with disease, differs from what might be expected. However, epidemiology also draws on methods from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioral sciences. In fact, epidemiology is often described as the basic science of public health, and for good reason. First, epidemiology is a quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods. Second, epidemiology is a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors, states, and events. However, epidemiology is not just a research activity but an integral component of public health, providing the foundation for directing practical and appropriate public health action based on this science and causal reasoning.2 UE 1.2.S2 - Épidémiologie

7 « Distribution » Fréquence et répartition des événements de santé
Fréquence: nombre des événements dans population, taux ou risque de la maladie dans population. Taux: nombre des événements dans population divisé par la taille de la population, permet des comparaisons entre populations. Répartition: survenue des événements en rapport avec la santé, dans le temps, dans l’espace et selon les caractéristiques des personnes touchées. Epidemiology is concerned with the frequency and pattern of health events in a population: Frequency refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population, but also to the relationship of that number to the size of the population. The resulting rate allows epidemiologists to compare disease occurrence across different populations. Pattern refers to the occurrence of health-related events by time, place, and person. Time patterns may be annual, seasonal, weekly, daily, hourly, weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence. Place patterns include geographic variation, urban/rural differences, and location of work sites or schools. Personal characteristics include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures. Characterizing health events by time, place, and person are activities of descriptive epidemiology, discussed in more detail later in this lesson. UE 1.2.S2 - Épidémiologie

8 « Déterminants » Pourquoi et Comment
comparer groupes manifestant des taux différents et présentant des différences en termes de caractéristiques démographiques, génétiques ou immunologiques, de comportements, d’expositions environnantes, et d’autres « facteurs de risque ». Epidemiology is also used to search for determinants, which are the causes and other factors that influence the occurrence of disease and other health-related events. Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events. They assess whether groups with different rates of disease differ in their demographic characteristics, genetic or immunologic make-up, behaviors, environmental exposures, or other so-called potential risk factors. Ideally, the findings provide sufficient evidence to direct prompt and effective public health control and prevention measures. UE 1.2.S2 - Épidémiologie

9 « Etats ou événements liés à la santé »
Epidémies de maladies contagieuses Maladies endémiques (contagieuses ou non) Maladies chroniques Accidents et blessures Défauts congénitaux Problèmes de santé maternelle et infantile Santé au travail Santé et environnement Comportements en rapport avec santé Epidemiology was originally focused exclusively on epidemics of communicable diseases3 but was subsequently expanded to address endemic communicable diseases and non-communicable infectious diseases. By the middle of the 20th Century, additional epidemiologic methods had been developed and applied to chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health. Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use. Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk. Indeed, the term health- related states or events may be seen as anything that affects the well-being of a population. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health-related states and events that are studied. UE 1.2.S2 - Épidémiologie

10 « Populations spécifiques »
Démarche clinique Démarche de santé publique Santé de l’individu Signes cliniques Rechercher des causes Examens complémentaires Diagnostic Traiter pour soigner ou guérir Surveiller Santé d’une population Identifier un phénomène de santé Formuler des hypothèses / rechercher des causes Enquête épidémiologique Analyser les résultats et la communiquer Prendre des mesure des santé publique Veille épidémiologique / analyser impact de l’intervention Although epidemiologists and direct health-care providers (clinicians) are both concerned with occurrence and control of disease, they differ greatly in how they view “the patient.” The clinician is concerned about the health of an individual; the epidemiologist is concerned about the collective health of the people in a community or population. In other words, the clinician’s “patient” is the individual; the epidemiologist’s “patient” is the community. Therefore, the clinician and the epidemiologist have different responsibilities when faced with a person with illness. For example, when a patient with diarrheal disease presents, both are interested in establishing the correct diagnosis. However, while the clinician usually focuses on treating and caring for the individual, the epidemiologist focuses on identifying the exposure or source that caused the illness; the number of other persons who may have been similarly exposed; the potential for further spread in the community; and interventions to prevent additional cases or recurrences. UE 1.2.S2 - Épidémiologie

11 « Application pour le contrôle des problèmes de santé »
Davantage que la simple « étude de … » Objectif: promouvoir, protéger, restaurer santé Les résultats servent à guider l’action de santé publique au niveau de la population Implique expérience et créativité (art) lors de la planification des mesure de contrôle et de prévention Epidemiology is not just “the study of” health in a population; it also involves applying the knowledge gained by the studies to community-based practice. Like the practice of medicine, the practice of epidemiology is both a science and an art. To make the proper diagnosis and prescribe appropriate treatment for a patient, the clinician combines medical (scientific) knowledge with experience, clinical judgment, and understanding of the patient. Similarly, the epidemiologist uses the scientific methods of Introduction to Epidemiology Page 1-4 descriptive and analytic epidemiology as well as experience, epidemiologic judgment, and understanding of local conditions in “diagnosing” the health of a community and proposing appropriate, practical, and acceptable public health interventions to control and prevent disease in the community. UE 1.2.S2 - Épidémiologie

12 Définition “L’épidémiologie est l’étude de la distribution et des déterminants des états ou des événements liés à la santé dans des populations spécifiques, et l’application de cette connaissance pour le contrôle des problèmes de santé.” Last JM, editor. Dictionary of epidemiology. 4th ed. New York: Oxford University Press; p. 61. Epidemiology is the study (scientific, systematic, data-driven) of the distribution (frequency, pattern) and determinants (causes, risk factors) of health-related states and events (not just diseases) in specified populations (patient is community, individuals viewed collectively), and the application of (since epidemiology is a discipline within public health) this study to the control of health problems. UE 1.2.S2 - Épidémiologie

13 Introduction à l’épidémiologie
2. HISTORIQUE

14 Deux périodes Avant 1940 Après 1940 UE 1.2.S2 - Épidémiologie

15 Hippocrate « Celui qui veut approfondir la médecine doit faire ce qui suit : Il considérera d’abord les saisons de l’année […] ; puis il examinera quels sont les vents chauds et froids, surtout ceux qui sont communs à tous les pays, ensuite ceux qui sont propres à chaque localité. […] Il acquerra des notions très précises sur la nature des eaux dont les habitants font usage […]; il étudiera les divers états du sol […]. Il reconnaîtra le genre de vie des habitants, qui sont ou amis du vin, de la bonne chère et du repos, ou laborieux, adonnés aux exercices du corps, mangeant beaucoup et buvant peu. » Hippocrates attempted to explain disease occurrence from a rational rather than a supernatural viewpoint. In his essay entitled “On Airs, Waters, and Places,” Hippocrates suggested that environmental and host factors such as behaviors might influence the development of disease. av. J.-C. UE 1.2.S2 - Épidémiologie

16 John Graunt Mercier (1620 – 1674) 1662
Another early contributor to epidemiology was John Graunt, a London haberdasher and councilman who published a landmark analysis of mortality data in This publication was the first to quantify patterns of birth, death, and disease occurrence, noting disparities between males and females, high infant mortality, urban/rural differences, and seasonal variations.5 Mercier (1620 – 1674) UE 1.2.S2 - Épidémiologie

17 Table de mortalité UE 1.2.S2 - Épidémiologie

18 William Farr Système de compilation de routine du nombre et de la cause des décès Pendant 40 ans: tradition de collecte et application minutieuse des statistiques vitales aux problèmes de santé Modèles mathématiques de la crue et décrue des épidémies Etat civil, profession, altitude 1800 William Farr built upon Graunt’s work by systematically collecting and analyzing Britain’s mortality statistics. Farr, considered the father of modern vital statistics and surveillance, developed many of the basic practices used today in vital statistics and disease classification. He concentrated his efforts on collecting vital statistics, assembling and evaluating those data, and reporting to responsible health authorities and the general public.4 Médecin – statisticien (1807 – 1883) Bureau du registre général UE 1.2.S2 - Épidémiologie

19 John Snow (1813-1858) médecin – anesthésiste 1854
In the mid-1800s, an anesthesiologist named John Snow was conducting a series of investigations in London that warrant his being considered the “father of field epidemiology.” Twenty years before the development of the microscope, Snow conducted studies of cholera outbreaks both to discover the cause of disease and to prevent its recurrence. Because his work illustrates the classic sequence from descriptive epidemiology to hypothesis generation to hypothesis testing (analytic epidemiology) to application, two of his investigations will be described in detail. UE 1.2.S2 - Épidémiologie

20 Pompe à Broad Street (cc) Justin Cormack
Snow conducted one of his now famous studies in 1854 when an epidemic of cholera erupted in the Golden Square of London.5 He began his investigation by determining where in this area persons with cholera lived and worked. He marked each residence on a map of the area, as shown in Figure 1.1. Today, this type of map, showing the geographic distribution of cases, is called a spot map. Because Snow believed that water was a source of infection for cholera, he marked the location of water pumps on his spot map, then looked for a relationship between the distribution of households with cases of cholera and the location of pumps. He noticed that more case households clustered around Pump A, the Broad Street pump, than around Pump B or C. When he questioned residents who lived in the Golden Square area, he was told that they avoided Pump B because it was grossly contaminated, and that Pump C was located too inconveniently for most of them. From this information, Snow concluded that the Broad Street pump (Pump A) was the primary source of water and the most likely source of infection for most persons with cholera in the Golden Square area. He noted with curiosity, however, that no cases of cholera had occurred in a two-block area just to the east of the Broad Street pump. Upon investigating, Snow found a brewery located there with a deep well on the premises. Brewery workers got their water from this well, and also received a daily portion of Introduction to Epidemiology Page 1-8 malt liquor. Access to these uncontaminated rations could explain why none of the brewery’s employees contracted cholera. To confirm that the Broad Street pump was the source of the epidemic, Snow gathered information on where persons with cholera had obtained their water. Consumption of water from the Broad Street pump was the one common factor among the cholera patients. After Snow presented his findings to municipal officials, the handle of the pump was removed and the outbreak ended. The site of the pump is now marked by a plaque mounted on the wall outside of the appropriately named John Snow Pub. Figure 1.2 John Snow Pub, London Source: The John Snow Society [Internet]. London: [updated 2005 Oct 14; cited 2006 Feb 6]. Available from: (cc) Justin Cormack UE 1.2.S2 - Épidémiologie

21 La grande expérience, 1854 Snow’s second investigation reexamined data from the 1854 cholera outbreak in London. During a cholera epidemic a few years earlier, Snow had noted that districts with the highest death rates were serviced by two water companies: the Lambeth Company and the Southwark and Vauxhall Company. At that time, both companies obtained water from the Thames River at intake points that were downstream from London and thus susceptible to contamination from London sewage, which was discharged directly into the Thames. To avoid contamination by London sewage, in 1852 the Lambeth Company moved its intake water works to a site on the Thames well upstream from London. Over a 7-week period during the summer of 1854, Snow compared cholera mortality among districts that received water from one or the other or both water companies. The results are shown in Table 1.1. The data in Table 1.1 show that the cholera death rate was more than 5 times higher in districts served only by the Southwark and Vauxhall Company (intake downstream from London) than in those served only by the Lambeth Company (intake upstream from London). Interestingly, the mortality rate in districts supplied by both companies fell between the rates for districts served exclusively by either company. These data were consistent with the hypothesis that water obtained from the Thames below London was a source of cholera. Alternatively, the populations supplied by the two companies may have differed on other factors that affected their risk of cholera. To test his water supply hypothesis, Snow focused on the districts served by both companies, because the households within a district were generally comparable except for the water supply company. In these districts, Snow identified the water supply company for every house in which a death from cholera had occurred during the 7-week period. Table 1.2 shows his findings. Quartier desservis par Population Nombre de décès par choléra Taux de mortalité pour 1000 hab. Southwark et Vauxhall 844 5.0 Lambeth 19 133 18 0.9 Les deux 652 2.2 UE 1.2.S2 - Épidémiologie

22 La grande expérience, 1854 Table 1.2 This study, demonstrating a higher death rate from cholera among households served by the Southwark and Vauxhall Company in the mixed districts, added support to Snow’s hypothesis. It also established the sequence of steps used by current-day epidemiologists to investigate outbreaks of disease. Based on a characterization of the cases and population at risk by time, place, and person, Snow developed a testable hypothesis. He then tested his hypothesis with a more rigorously designed study, ensuring that the groups to be compared were comparable. After this study, efforts to control the epidemic were directed at changing the location of the water intake of the Southwark and Vauxhall Company to avoid sources of contamination. Thus, with no knowledge of the existence of microorganisms, Snow demonstrated through epidemiologic studies that water could serve as a vehicle for transmitting cholera and that epidemiologic information could be used to direct prompt and appropriate public health action. Maisons desservis par Population Nombre de décès par choléra Taux de mortalité pour 1000 hab. Southwark et Vauxhall 98 852 419 4.2 Lambeth 80 0.5 UE 1.2.S2 - Épidémiologie

23 A partir de 1940 Epidémiologie dépasse le cadre des maladies infectieuses Utilisation de méthode modernes de l’épidémiologie In the mid- and late-1800s, epidemiological methods began to be applied in the investigation of disease occurrence. At that time, most investigators focused on acute infectious diseases. In the 1930s and 1940s, epidemiologists extended their methods to noninfectious diseases. The period since World War II has seen an explosion in the development of research methods and the theoretical underpinnings of epidemiology. Epidemiology has been applied to the entire range of health-related outcomes, behaviors, and even knowledge and attitudes. The studies by Doll and Hill linking lung cancer to smoking6and the study of cardiovascular disease among residents of Framingham, Massachusetts7 are two examples of how pioneering researchers have applied epidemiologic methods to chronic disease since World War II. During the 1960s and early 1970s health workers applied epidemiologic methods to eradicate naturally occurring smallpox worldwide.8 This was an achievement in applied epidemiology of unprecedented proportions. In the 1980s, epidemiology was extended to the studies of injuries and violence. In the 1990s, the related fields of molecular and genetic epidemiology (expansion of epidemiology to look at specific pathways, molecules and genes that influence risk of developing disease) took root. Meanwhile, infectious diseases continued to challenge epidemiologists as new infectious agents emerged (Ebola virus, Human Immunodeficiency virus (HIV)/ Acquired Immunodeficiency Syndrome (AIDS)), were identified (Legionella, Severe Acute Respiratory Syndrome (SARS)), or changed (drug-resistant Mycobacterium tuberculosis, Avian influenza). Beginning in the 1990s and accelerating after the terrorist attacks of September 11, 2001, epidemiologists have had to consider not only natural transmission of infectious organisms but also deliberate spread through biologic warfare and bioterrorism. Today, public health workers throughout the world accept and use epidemiology regularly to characterize the health of their communities and to solve day-to-day problems, large and small. UE 1.2.S2 - Épidémiologie

24 Cohorte Framingham Ville de Framingham, Massachusetts (USA)
5200 habitants sains, suivis depuis 1948 sur plus de 5 décennies Récolte de nombreuses caractéristiques d’intérêt (« facteurs de risques ») pour l’étude d’une ou de plusieurs maladies framinghamheartstudy.org UE 1.2.S2 - Épidémiologie

25 Richard Doll et Austin Bradford Hill
Comment expliquer «l’épidémie» de cancers broncho-pulmonaires chez les hommes d'âge moyen ? Augmentation progressive mais persistante des cancers broncho-pulmonaires depuis 1930 (recueil systématique des cas dans les hôpitaux de Londres…) UE 1.2.S2 - Épidémiologie

26 Richard Doll et Austin Bradford Hill
Etude cas-témoin Etude de cohorte Première étude : un des prototypes des enquêtes cas-témoins : 1 500 cas comparés à témoins de même âge et même sexe (appariés) 1ère publication en 1950 : Tabac = principal facteur associé à la survenue des cancers broncho-pulmonaires Mais : n’emporte pas la conviction générale (parlement anglais) De 1951 à 1954 : première étude longitudinale : médecins de Grande Bretagne suivis pendant 2 ans pour comparer la fréquence des cancers broncho-pulmonaires entre fumeurs et non fumeurs Lien de causalité Tabac - cancer broncho-pulmonaire enfin retenu à l’issue de cette étude UE 1.2.S2 - Épidémiologie

27 3. Utilisations de l’épidémiologie
Introduction à l’épidémiologie 3. Utilisations de l’épidémiologie

28 Utilisation de l’épidémiologie
Evaluation de la santé d’une population ou d’une communauté́ Quels sont les problèmes actuels ou potentiels ? Quels services sont disponibles, accessibles, efficaces, économiques ? Décisions individuelles Arrêter de fumer? Prendre l’escalier ? Utiliser un préservatif ? Commander une salade? Compléter le tableau clinique Rechercher les causes Ensemble avec d’autres disciplines Epidemiology and the information generated by epidemiologic methods have been used in many ways.9 Some common uses are described below. Assessing the community’s health Public health officials responsible for policy development, implementation, and evaluation use epidemiologic information as a factual framework for decision making. To assess the health of a population or community, relevant sources of data must be identified and analyzed by person, place, and time (descriptive epidemiology). What are the actual and potential health problems in the community? Where are they occurring? Which populations are at increased risk? Which problems have declined over time? Which ones are increasing or have the potential to increase? How do these patterns relate to the level and distribution of public health services available? More detailed data may need to be collected and analyzed to determine whether health services are available, accessible, effective, and efficient. For example, public health officials used epidemiologic data and methods to identify baselines, to set health goals for the nation in 2000 and 2010, and to monitor progress toward these goals.10-12 Making individual decisions Many individuals may not realize that they use epidemiologic information to make daily decisions affecting their health. When persons decide to quit smoking, climb the stairs rather than wait for an elevator, eat a salad rather than a cheeseburger with fries for lunch, or use a condom, they may be influenced, consciously or unconsciously, by epidemiologists’ assessment of risk. Since World War II, epidemiologists have provided information related to all those decisions. In the 1950s, epidemiologists reported the increased risk of lung cancer among smokers. In the 1970s, epidemiologists documented the role of exercise and proper diet in reducing the risk of heart disease. In the mid-1980s, epidemiologists identified the increased risk of HIV infection associated with certain sexual and drug-related behaviors. These and hundreds of other epidemiologic findings are directly relevant to the choices people make every day, choices that affect their health over a lifetime. Introduction to Epidemiology Page 1-12 Completing the clinical picture When investigating a disease outbreak, epidemiologists rely on health-care providers and laboratorians to establish the proper diagnosis of individual patients. But epidemiologists also contribute to physicians’ understanding of the clinical picture and natural history of disease. For example, in late 1989, a physician saw three patients with unexplained eosinophilia (an increase in the number of a specific type of white blood cell called an eosinophil) and myalgias (severe muscle pains). Although the physician could not make a definitive diagnosis, he notified public health authorities. Within weeks, epidemiologists had identified enough other cases to characterize the spectrum and course of the illness that came to be known as eosinophilia-myalgia syndrome.13 More recently, epidemiologists, clinicians, and researchers around the world have collaborated to characterize SARS, a disease caused by a new type of coronavirus that emerged in China in late Epidemiology has also been instrumental in characterizing many non-acute diseases, such as the numerous conditions associated with cigarette smoking — from pulmonary and heart disease to lip, throat, and lung cancer. Searching for causes Much epidemiologic research is devoted to searching for causal factors that influence one’s risk of disease. Ideally, the goal is to identify a cause so that appropriate public health action might be taken. One can argue that epidemiology can never prove a causal relationship between an exposure and a disease, since much of epidemiology is based on ecologic reasoning. Nevertheless, epidemiology often provides enough information to support effective action. Examples date from the removal of the handle from the Broad St. pump following John Snow’s investigation of cholera in the Golden Square area of London in 1854,5 to the withdrawal of a vaccine against rotavirus in 1999 after epidemiologists found that it increased the risk of intussusception, a potentially life-threatening condition.15 Just as often, epidemiology and laboratory science converge to provide the evidence needed to establish causation. For example, epidemiologists were able to identify a variety of risk factors during an outbreak of pneumonia among persons attending the American Legion Convention in Philadelphia in 1976, even though the Legionnaires’ bacillus was not identified in the laboratory from lung tissue of a person who had died from Legionnaires’ disease until almost 6 months later.16 UE 1.2.S2 - Épidémiologie

29 Les grandes fonctions de l’épidémiologie
Surveillance, mesurer l’état de santé de la population Enquêtes de terrain Épidémiologie descriptive Etudes analytiques Épidémiologie étiologique Evaluation des intervention Épidémiologie évaluative Mise en place de politique de santé plus efficace In the mid-1980s, five major tasks of epidemiology in public health practice were identified: public health surveillance, field investigation, analytic studies, evaluation. policy development, was recently added. These tasks are described below. Public health surveillance Public health surveillance is the ongoing, systematic collection, analysis, interpretation, and dissemination of health data to help guide public health decision making and action. Surveillance is equivalent to monitoring the pulse of the community. The purpose of public health surveillance, which is sometimes called “information for action,”18 is to portray the ongoing patterns of disease occurrence and disease potential so that investigation, control, and prevention measures can be applied efficiently and effectively. This is accomplished through the systematic collection and evaluation of morbidity and mortality reports and other relevant health information, and the dissemination of these data and their interpretation to those involved in disease control and public health decision making. Morbidity and mortality reports are common sources of surveillance data for local and state health departments. These reports generally are submitted by health-care providers, infection control practitioners, or laboratories that are required to notify the health department of any patient with a reportable disease such as pertussis, meningococcal meningitis, or AIDS. Other sources of health-related data that are used for surveillance include reports from investigations of individual cases and disease clusters, public health program data such as immunization coverage in a community, disease registries, and health surveys. Most often, surveillance relies on simple systems to collect a limited amount of information about each case. Although not every case of disease is reported, health officials regularly review the case reports they do receive and look for patterns among them. These practices have proven invaluable in detecting problems, evaluating programs, and guiding public health action. While public health surveillance traditionally has focused on communicable diseases, surveillance systems now exist that target injuries, chronic diseases, genetic and birth defects, occupational and potentially environmentally-related diseases, and health behaviors. Since September 11, 2001, a variety of systems that rely on electronic reporting have been developed, including those that report daily emergency department visits, sales of over-the-counter medicines, and worker absenteeism.19,20 Because epidemiologists are likely to be called upon to design and use these and other new surveillance systems, an epidemiologist’s core competencies must include design of data collection instruments, data management, descriptive methods and graphing, interpretation of data, and scientific writing and presentation. Field investigation As noted above, surveillance provides information for action. One of the first actions that results from a surveillance case report or report of a cluster is investigation by the public health department. The investigation may be as limited as a phone call to the health- care provider to confirm or clarify the circumstances of the reported case, or it may involve a field investigation requiring the coordinated efforts of dozens of people to characterize the extent of an epidemic and to identify its cause. The objectives of such investigations also vary. Investigations often lead to the identification of additional unreported or unrecognized ill persons who might otherwise continue to spread infection to others. For example, one of the hallmarks of investigations of persons with sexually transmitted disease is the identification of sexual partners or contacts of patients. When interviewed, many of these contacts are found to be infected without knowing it, and are given treatment they did not realize they needed. Identification and treatment of these contacts prevents further spread. For some diseases, investigations may identify a source or vehicle of infection that can be controlled or eliminated. For example, the investigation of a case of Escherichia coli O157:H7 infection usually focuses on trying to identify the vehicle, often ground beef but sometimes something more unusual such as fruit juice. By identifying the vehicle, investigators may be able to determine how many other persons might have already been exposed and how many continue to be at risk. When a commercial product turns out to be the culprit, public announcements and recalling the product may prevent many additional cases. Occasionally, the objective of an investigation may simply be to learn more about the natural history, clinical spectrum, descriptive epidemiology, and risk factors of the disease before determining what disease intervention methods might be appropriate. Early investigations of the epidemic of SARS in 2003 were needed to establish a case definition based on the clinical presentation, and to characterize the populations at risk by time, place, and person. As more was learned about the epidemiology of the disease and communicability of the virus, appropriate recommendations regarding isolation and quarantine were issued.21 Field investigations of the type described above are sometimes referred to as “shoe leather epidemiology,” conjuring up images of dedicated, if haggard, epidemiologists beating the pavement in search of additional cases and clues regarding source and mode of transmission. This approach is commemorated in the symbol of the Epidemic Intelligence Service (EIS), CDC’s training program for disease detectives — a shoe with a hole in the sole. Analytic studies Surveillance and field investigations are usually sufficient to identify causes, modes of transmission, and appropriate control and prevention measures. But sometimes analytic studies employing more rigorous methods are needed. Often the methods are used in combination — with surveillance and field investigations providing clues or hypotheses about causes and modes of transmission, and analytic studies evaluating the credibility of those hypotheses. Clusters or outbreaks of disease frequently are investigated initially with descriptive epidemiology. The descriptive approach involves the study of disease incidence and distribution by time, place, and person. It includes the calculation of rates and identification of parts of the population at higher risk than others. Occasionally, when the association between exposure and disease is quite strong, the investigation may stop when descriptive epidemiology is complete and control measures may be implemented immediately. John Snow’s 1854 investigation of cholera is an example. More frequently, descriptive studies, like case investigations, generate hypotheses that can be tested with analytic studies. While some field investigations are conducted in response to acute health problems such as outbreaks, many others are planned studies. The hallmark of an analytic epidemiologic study is the use of a valid comparison group. Epidemiologists must be skilled in all aspects of such studies, including design, conduct, analysis, interpretation, and communication of findings. Design includes determining the appropriate research strategy and study design, writing justifications and protocols, calculating sample sizes, deciding on criteria for subject selection (e.g., developing case definitions), choosing an appropriate comparison group, and designing questionnaires. Conduct involves securing appropriate clearances and approvals, adhering to appropriate ethical principles, abstracting records, tracking down and interviewing subjects, collecting and handling specimens, and managing the data. Analysis begins with describing the characteristics of the subjects. It progresses to calculation of rates, creation of comparative tables (e.g., two-by-two tables), and computation of measures of association (e.g., risk ratios or odds ratios), tests of significance (e.g., chi-square test), confidence intervals, and the like. Many epidemiologic studies require more advanced analytic techniques such as stratified analysis, regression, and modeling. Finally, interpretation involves putting the study findings into perspective, identifying the key take-home messages, and making sound recommendations. Doing so requires that the epidemiologist be knowledgeable about the subject matter and the strengths and weaknesses of the study. Evaluation Epidemiologists, who are accustomed to using systematic and quantitative approaches, have come to play an important role in evaluation of public health services and other activities. Evaluation is the process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency, and impact of activities with respect to established goals. Effectiveness refers to the ability of a program to produce the intended or expected results in the field; effectiveness differs from efficacy, which is the ability to produce results under ideal conditions. Efficiency refers to the ability of the program to produce the intended results with a minimum expenditure of time and resources. The evaluation itself may focus on plans (formative evaluation), operations (process evaluation), impact (summative evaluation), or outcomes — or any combination of these. Evaluation of an immunization program, for example, might assess the efficiency of the operations, the proportion of the target population immunized, and the apparent impact of the program on the incidence of vaccine-preventable diseases. Similarly, evaluation of a surveillance system might address operations and attributes of the system, its ability to detect cases or outbreaks, and its usefulness. Policy development The definition of epidemiology ends with the following phrase: “...and the application of this study to the control of health problems.” While some academically minded epidemiologists have stated that epidemiologists should stick to research and not get involved in policy development or even make recommendations,24 public health epidemiologists do not have this luxury. Indeed, epidemiologists who understand a problem and the population in which it occurs are often in a uniquely qualified position to recommend appropriate interventions. As a result, epidemiologists working in public health regularly provide input, testimony, and recommendations regarding disease control strategies, reportable disease regulations, and health-care policy. UE 1.2.S2 - Épidémiologie

30 Démarche en Santé Publique
Demandes Besoins Réponses En cela l’epidemiologie s’inscrit dans la demaches de sante publique a plusieurs niveaux: elle contribue a la detection la mise en evidence de besoins mais aussi a proposer et tester l’efficacite des eventuelles reponses a ces besoins. Par exemple: Epidémiologie UE 1.2.S2 - Épidémiologie

31  3 branches de l’épidémiologie :
“L’épidémiologie est l’étude de la distribution et des déterminants des états ou des événements liés à la santé dans des populations spécifiques, et l’application de cette connaissance pour le contrôle des problèmes de santé.”  3 branches de l’épidémiologie : Descriptive Analytique ou étiologique Évaluative UE 1.2.S2 - Épidémiologie

32 4. LES BRANCHES DE L’épidémiologie
Introduction à l’épidémiologie 4. LES BRANCHES DE L’épidémiologie UE 1.2.S2 - Épidémiologie

33 Les Branches de l’épidémiologie
Épidémiologie descriptive Décrire l’état de santé d’une population Épidémiologie analytique Rechercher les causes / les déterminants d’un problème de santé Épidémiologie évaluative Évaluer l’efficacité des interventions UE 1.2.S2 - Épidémiologie

34 Les Branches de l’épidémiologie
Épidémiologie descriptive Décrire l’état de santé d’une population Épidémiologie analytique Rechercher les causes / les déterminants d’un problème de santé Épidémiologie évaluative Évaluer l’efficacité des interventions UE 1.2.S2 - Épidémiologie

35 Indicateurs de fréquence
Incidence Nombre de nouveaux cas d’une maladie ou un problème de santé apparu pendant une période de temps au sein d’une population Nombre de cas de grippe en Franche Comté le mois dernier. Prévalence Proportion de personnes affectées par un problème de santé dans la population qui présentent cette maladie, à un moment donné. Exemple: nombre total de personnes atteinte d’hépatite C en France aujourd’hui. Taux Mesure de fréquence d’un phénomène par unité de temps dans une population Exemple: taux de mortalité = nombre de décès par an. Taux de survenue du cancer du poumon en 2012. As with all scientific endeavors, the practice of epidemiology relies on a systematic approach. In very simple terms, the epidemiologist: Counts cases or health events, and describes them in terms of time, place, and person; Divides the number of cases by an appropriate denominator to calculate rates; and Compares these rates over time or for different groups of people. UE 1.2.S2 - Épidémiologie

36 Distribution Étudier les VARIATIONS de fréquence en fonction :
des CARACTÉRISTIQUES DES PERSONNES âge, sexe, profession, comportements, etc… de leur RÉPARTITION GÉOGRAPHIQUE (pays, région, communes, etc..) et de leur ENVIRONNEMENT : Pays, différences urbain-rural, le lieu de travail, l’emplacement des écoles, etc. Exemple: Incidence cancer de l’œsophage : 300 fois plus élevé en Iran qu’au Niger de leur évolution DANS LE TEMPS : survenue annuelle, saisonnière, journalière (voire par heure) pendant une épidémie. Exemple: en France, depuis 1985, augmentation parallèle de la consommation de tabac et mortalité par cancer du poumon UE 1.2.S2 - Épidémiologie

37 Temps Exemple de distribution saisonnière du virus de la grippe.
Pic d’incidence entre Novembre et Mars chaque année. UE 1.2.S2 - Épidémiologie

38 Epidémiologie Descriptive
Permet une meilleure connaissance des besoins de prise en charge médicale Exemple : Prévalence des trisomies 21 et âge de la mère Âge de la mère entre 20 et 25 ans : risque de trisomie < 1 ‰ Entre 25 et 30 ans : augmentation lente du risque à 29 ans : risque > 1 ‰ à 41 ans : risque de 1 % à 48 ans : risque de 10 % D’où la mise en place des mesures suivantes : Diagnostic prénatal systématique par amniocentèse et caryotype du fœtus chez les femmes de 38 ans et plus UE 1.2.S2 - Épidémiologie

39 Méthodes en épidémiologie descriptive
Etudes observationnelles Etudes transversales (un jour donné) Mesure de la prévalence des infections nosocomiales dans un service hospitalier ou un hôpital Etudes longitudinales dans le temps (incidence) Mesure de l’incidence de survenue des cancers chaque année UE 1.2.S2 - Épidémiologie

40 Les Branches de l’épidémiologie
Épidémiologie descriptive Décrire l’état de santé d’une population Épidémiologie analytique Rechercher les causes / les déterminants d’un problème de santé Épidémiologie évaluative Évaluer l’efficacité des interventions UE 1.2.S2 - Épidémiologie

41 Epidémiologie Analytique
RECHERCHER LES CAUSES DES PROBLÈMES DE SANTÉ : Étudier l’association entre facteurs de risque et maladie Définir l’impact de l'exposition à des FACTEURS pouvant jouer un rôle dans l'apparition d’une maladie Exemples d’étude de la relation entre exposition (soupçonnée d’avoir un rôle causal) et maladie : Pollution et asthme Activité physique et ostéoporose (rôle protecteur) Classe sociale et surmortalité (Marqueurs de risque) UE 1.2.S2 - Épidémiologie

42 Epidémiologie Analytique
MÉTHODE: 2 types d’enquête permettant des comparaisons: Comparer la fréquence d’apparition de la maladie entre sujets exposés et non exposés à un facteur: Enquête exposés - non exposés = enquête de cohorte Comparer la fréquence de l'exposition à des facteurs de risque entre des sujets malades et des sujets indemnes de la maladie: Enquête cas - témoins UE 1.2.S2 - Épidémiologie

43 Méthodes Etude cas-témoins Etude de cohorte
Étude de la relation entre une malformation congénitale et exposition aux pesticides pendant la grossesse Etude cas-témoins Etude de cohorte Interroger les mères d’enfants malformés et d’enfants normaux sur leurs expositions aux pesticides pendant la grossesse Suivre 2 groupes de femmes : l’un exposé aux pesticides, l’autre non et comparer la fréquence des malformations dans les deux groupes Parler des avantages des études de cohortes et de la notion de biais Etude transversale étiologique UE 1.2.S2 - Épidémiologie

44 Notion de risque Risque Relatif Odds ratio
Mesure de la force de l’association entre une exposition à un facteur de risque et le risque de survenue de la maladie lié à cette exposition RR = Risque groupe exposé / risque groupe non exposé Obtenu dans les études de cohortes = Rapport des cotes/des chances Estimation du risque relatif Calculé à l’issue d’une enquête cas-témoins UE 1.2.S2 - Épidémiologie

45 Les Branches de l’épidémiologie
Épidémiologie descriptive Décrire l’état de santé d’une population Épidémiologie analytique Rechercher les causes / les déterminants d’un problème de santé Épidémiologie évaluative Évaluer l’efficacité des interventions UE 1.2.S2 - Épidémiologie

46 Epidémiologie Evaluative
Évaluer LES ACTIONS de santé (préventives et curatives) dans la collectivité Mesurer LES EFFETS d’une action de santé par rapport aux objectifs fixés:  Aide à la prise de décision pour la PLANIFICATION UE 1.2.S2 - Épidémiologie

47 Epidémiologie Evaluative
PRINCIPAUX ASPECTS: Évaluation de techniques ou de stratégies diagnostiques et thérapeutiques pour déterminer la plus adaptée Évaluation de nouvelles techniques d’examen ou de nouveaux traitements (essai thérapeutique) Évaluation de la qualité des soins Évaluation a posteriori de l’impact des actions de santé (évaluation avant-après) par rapport aux objectifs fixés UE 1.2.S2 - Épidémiologie

48 Méthodes en épidémiologie évaluative
Etudes expérimentales Comparaisons avant/après intervention Essais thérapeutiques randomisés UE 1.2.S2 - Épidémiologie

49 Niveau de preuve scientifique en épidémiologie
1 Essai clinique randomisé 2 Etude de cohorte 3 Etude cas témoin 4 Etude transversale

50 5. Questions éthiques Introduction à l’épidémiologie
UE 1.2.S2 - Épidémiologie

51 Principes éthiques en épidémiologie
4 grands principes Respect des individus Faire le bien Ne pas nuire Etre juste Respecter: Parler des implications pour les essais cliniques Information eclairee / consentement participation / Protection des données Ne pas nuire: physiquement et psychologiquement Tres vrai dans etudes observationnelle ou il n’y a aucun bénéfice immédiat attendu. UE 1.2.S2 - Épidémiologie

52 Important en particulier pour:
Essais thérapeutiques (études épidémiologiques expérimentales). Régis par les Lois de bioéthique. Epidémiologie en tant qu’outil pour la prise de décision en politique de santé

53 6. Le rôle de l’infirmier Introduction à l’épidémiologie
UE 1.2.S2 - Épidémiologie

54 Le rôle de l’infirmier en épidémiologie
Décrire les phénomènes de santé Aide à la surveillance d’épidémies Etude de fréquence des infections nosocomiales à l’hôpital Suivi du saturnisme en PMI Enquête de santé des salariés en santé pour un(e) infirmièr(e) en santé du travail. Rechercher les causes Participation à la recherche en épidémiologie en tant qu’infirmière de recherche clinique C'est la personne qui donne des soins infirmiers et des services de santé notamment en milieu scolaire en vue de favoriser l'adoption de saines habitudes. A cette fin, elle conçoit des programmes de santé adaptés aux besoins des jeunes, offre des services de consultation individuelle, prépare des interventions éducatives de groupe au sujet de l'hygiène, des maladies et de leur prévention et administre les premiers soins en cas d'urgence. Elle se préoccupe de la santé globale des élèves et veille à donner le soutien nécessaire au personnel enseignant afin de favoriser l'auto responsabilisation des jeunes quant à leur santé. L’infirmier social assure le dépistage, la prévention, les soins, le développement de programmes communautaires, l’éducation pour la santé et des fonctions curatives, que ce soit dans le cadre d’une pratique individuelle ou en qualité de responsable ou de membre d’une équipe de travailleurs médico-sociaux. L’intervention de l’infirmier social se situe toujours dans le cadre d’un travail d’équipe pluridisciplinaire. Il est entouré de collègues psychologues et assistants sociaux. Toutefois, sa spécificité se situe surtout au niveau des tests médicaux portant sur les problèmes de vue ou d’ouïe qui peuvent compromettre le déroulement d’une bonne scolarité des enfants. Il joue également un rôle important au niveau d’une politique d’information à la santé vis-à-vis des enfants de l’école maternelle. Il participe à de nombreuses animations dans les écoles : ces animations concernent l’hygiène dentaire, les dangers domestiques, l’équilibre alimentaire, le sommeil, etc…. Petit éclairage sur un secteur d’intervention : en centre P.M.S. Le rôle de l’infirmier en centre P.M.S. se situe à tous les niveaux d’enseignement (maternel, primaire et secondaire). Il intervient surtout au niveau des classes de transition : c’est ainsi qu’en maternelle, l’équipe du P.M.S. concentre surtout ses efforts sur les enfants de 3eme maternelle. Cette équipe vérifie les capacités d’intégration et les aptitudes à accéder à l’enseignement fondamental. Les enfants sont soumis à des tests, à des animations sous forme de jeux pour sensibiliser à différents aspects inhérents à l’enseignement primaire. En ce qui concerne l’enseignement primaire, l’intervention se situe essentiellement au niveau des enfants de 6e primaire et a pour objet de les aider à appréhender une méthode de travail personnelle qui permette de mieux aborder l’enseignement secondaire. Quant à l’enseignement secondaire, l’équipe suit les enfants de 1ere année afin de vérifier leurs acquis primaires et leur intégration dans l’enseignement secondaire. Elle organise également des animations destinées aux adolescents et qui portent sur certains aspects rencontrés durant cette période de transition et de développement de l’affectivité.

55 Le rôle de l’infirmier en épidémiologie
Interventions en santé Education pour la santé (scolaire, des patients à l’hôpital,…) Participation aux essais thérapeutiques Concevoir des programmes de santé En particulier en milieu scolaire Relevé de paramètres sur les enfants en santé scolaire Dépistage de maladies infantiles Éducation pour la santé

56 Le rôle de l’infirmier en épidémiologie
La recherche en soins infirmiers Utilisation de la démarche épidémiologiques au même titre que dans la recherche biomédicale.

57 A retenir Epidémiologie = méthode de base en santé publique
« Patient » de l’épidémiologie = la population La démarche en épidémiologie Les branches de l’épidémiologie et les grands types d’études épidémiologiques qui correspondent Les niveaux de preuves des différents types d’études et la notion de biais UE 1.2.S2 - Épidémiologie

58 Bibliographie P Czernichow, J Chaperon, X. Le Contour. Epidémiologie, Abrégés, Masson, 2001. F Bourdillon, G Brucker, D Tabuteau, Traité de Santé Publique, Medecine Science Flammarion, 2004. « Principles of Epidemiology » Self-Study Course ss1000 offert par le CDC. B Burlet, K Le Neurès, C Siebert, Santé Publique, Economie de la santé, Les essentiels en IFSI, Masson, 2010. UE 1.2.S2 - Épidémiologie

59 Crédits Image Pompe à Broad Street (cc) Justin Cormack UE 1.2.S2 - Épidémiologie


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